I loved this show even though I was about 20 when it was on the air, Whitman Mayo as 'Grampa' was so sweet and such a surprise even in the 70's to see a African-American just portraying a paternal figure for all kids not just this or that group of children.
The music was also interesting and different for most children's shows in that it wasn't the typical sappy, saccharine type of music that many other shows for children had, This one deserves to take it's place next to other ground-breaking children's shows like 'Sesame Street' and the like. Possibly if 'That's Cat' had been on public television, it would have lasted longer and be better remembered by more people.
I have to admit though, every time I see Mr.Mayo in something, the memories of this little gem of a show just makes me smile and wish something like it was around today or at least release this on DVD. Hope springs eternal.